1. Field of the Invention
The invention relates to an image recording apparatus in which an inkjet printhead having nozzles and performing recording on a recoding medium by ejecting ink droplets from the nozzles is mounted.
2. Description of Related Art
There is conventionally known an image recording apparatus of a type in which an inkjet printhead which performs recording on a recording medium by ejecting ink droplets from nozzles thereof is mounted. In the image recording apparatus of such a type, to maintain an ejection performance thereof at a proper level, a maintenance operation is implemented to remove bubbles accumulated in the inkjet printhead, ink dried and solidified, and others, by sucking these undesired substances from the side of the nozzles. Hence, the image recording apparatus of the type usually has a maintenance portion at a position outside a recording area, within which the inkjet printhead performs recording on a recording medium while reciprocating or moving relatively to the recording medium, and near an end of a range of the reciprocation of the inkjet printhead.
The maintenance portion includes a cap that is brought into contact with, and away from, a nozzle surface where the nozzles are open. When the inkjet printhead is moved outside the recording area to a position where the cap is disposed, the cap is moved to the nozzle surface to cover the nozzle surface, and maintenance operations such as sucking operation is performed with a pump device connected to the cap. The cap is typically formed of an elastic material and includes a protruding portion that protrudes toward the nozzle surface such that when the protruding portion is in contact with the nozzle surface, the protruding portion surrounds open ends of the nozzles.
As the inkjet printhead mounted in the image recording apparatus, there is employed an inkjet printhead as disclosed in JP-A-2004-25636 (see FIG. 4), for instance, where a piezoelectric actuator is fixed on a back surface of a cavity unit formed by laminating a plurality of plates and having ink passages therein, as shown in FIG. 11 of the publication. The plates forming the cavity unit are seven plates including a nozzle plate through which a plurality of nozzles are formed in rows, a cavity plate in which a plurality of pressure chambers in communication with the respective nozzles are formed, and two manifold plates in which a plurality of common ink chambers from which ink is distributed to the pressure chambers are formed. Formed of the laminate of such plates, the cavity unit has the nozzles on a front side thereof, the pressure chambers on a backside thereof, and the common ink chambers between the nozzles and the pressure chambers. In the inkjet printhead disclosed in the publication, damper chambers are formed in a damper plate constituting bottom surfaces of the common ink chambers at positions corresponding to the common ink chambers.
In the inkjet printhead including the thus constructed cavity unit, each common ink chamber opens with a large opening area at a position near the nozzle surface, thereby decreasing a rigidity of a bottom portion under each common ink chamber, i.e., a wall disposed between the bottom surface of the common ink chamber and the nozzle surface.
Hence, in the technique of the publication, the rigidity of the bottom portion of the common ink chamber is enhanced by disposing another plate as a reinforcing plate directly on a backside of the nozzle plate. According to this arrangement, even when a cap is frequently brought into pressing contact, with a large force, with the nozzle surface for the above-mentioned maintenance operations, a deformation of the bottom portion of the common ink chamber that causes a defective ejection of ink droplet or damage of the cavity unit does not occur.
JP-A-2003-326712 (see FIGS. 7 and 11), for instance, discloses to laminate a plurality of plates such that a width of a common ink chamber progressively decreases toward a bottom portion, in order to enhance a rigidity of the bottom portion of the common ink chamber. By this arrangement, a sufficient mechanical strength against a pressing force from a cap in a maintenance operation is provided.
Meanwhile, there is a demand for reducing the width and thickness of the cavity unit to meet the tendency of reduction in the size and weight of the inkjet printhead.
However, the above-described arrangements, namely, the arrangement where the reinforcing plate is disposed directly on the back side of the nozzle plate, and the arrangement where a plurality of plates are so assembled that the width of the common ink chamber progressively decreases, suffers from a limitation in reducing the thickness, or a dimension in a direction of stacking or lamination of the plates, of the cavity unit. Thus, an improvement has been requested to reduce the size of the cavity unit.